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Re: Synsacrum

Elongation of the sacral series in pterosaurs is related to elongation of the
ilium, which in turn was caused by expansion of the aerobic leg musculature
in high metabolic rate pterosaurs. The fully quadrupedal ceratopsian
dinosaurs also had very long ilia supported by a long sacral series -
bipedalism is not the critical factor. If pterosaurs were bipeds like birds,
they should have had wings without supple fingers and fold up well clear of
the ground, almost all pterosaurs had arms that folded in such a manner that
they could reach the ground to walk on the "small" fingers, which are in all
but one spe
cies bigger than the 

toes!  Tailless p
terosaurs were about as well adapted to bipedalism as chimps - could do it
but normal gait was bipedal. Of course, giant pterosaurs probably ran
bipedally to take off.